The Four-Level Interchange at the junction of U.S. Route 101 (the Hollywood Freeway and Santa Ana Freeway) and State Route 110 (the Harbor Freeway and Arroyo Seco Parkway) is a stunning feat of modern engineering, with a style you might not have time to appreciate as you’re negotiating your lane change. Completed in 1949, the junction was the world’s first stack interchange, a multi-tiered structure that separates traffic heading in each direction in dedicated lanes.

The design was an improvement over the more sweeping cloverleaf interchange design for reasons of safety and space—sited as it was in a densely developed area of downtown Los Angeles, there was only so much room for this crucial junction.

The four-level reinforced concrete structure was designed by a team of engineers and built by the James I. Barnes Construction Company. Although it was finished in 1949, it was not put into full use until the freeways it served were completed in 1953. The interchange, sometimes called “The Stack,” was retrofitted after the 1994 Northridge earthquake and renamed the Bill Keene Memorial Interchange after the late local traffic and weather announcer in 2006. It is the only interchange in the region to be certified as a civil engineering landmark by the Society of Civil Engineers, and its robust elegance is a true aesthetic achievement. As the Los Angeles Times said in 1949, “It’s the most photogenic pile of cement in town.”